Amorphous carbon grains : laboratory measurements in the 2000 A - 40 μm range.

The authors present the results of transmission measurements performed in the range 2000 Å - 40 μm on submicronic amorphous carbon particles. Morphological analysis was performed by using electron microscopy to determine grain properties and size distributions. The extinction of the samples indicates the presence of a pronounced hump at 2400 - 2500 Å with the peak dependent on particle size. Its characteristics are discussed both intrinsically and by comparing them with the interstellar curve. An extinction law ≡λ^-1 is found to hold at wavelengths longward of 4500 Å in agreement with a previous work. Astronomical observations and theoretical calculations are recalled which suggest that amorphous carbon may be produced in space, mainly in regions such as the atmosphere of late-type stars, novae and supernovae.